Interventions to increase aerobic exercise in patients with obsessive compulsive disorder (OCD) represent a potentially useful yet unexplored strategy for ameliorating OCD symptomatology. There are currently no established exercise interventions for use with this population. The long-term objectives of this research program are to improve treatment options for persons with OCD, by: 1) establishing the efficacy of an aerobic exercise intervention for individuals with OCD, and 2) advancing knowledge of the relationship between aerobic exercise and OCD symptomatology. In a pilot study conducted by our research group, individuals (n=15) who had clinically significant residual symptoms despite receiving treatment for OCD experienced significant and clinically meaningful decreases in OCD symptoms following participation in a 12-week aerobic exercise intervention. Treatment gains were largely maintained over a 6-month follow-up. However, due to the lack of a control condition in this study, the treatment gains could not be attributed directly to the exercise intervention. This project represents a collaboration among researchers with considerable experience in both the treatment of OCD and the application of exercise-based interventions. One hundred and two (102) patients with OCD with clinically significant OCD symptoms despite engaging in recommended treatment (pharmacotherapy or CBT) will be randomly assigned to receive either a 12-week moderate intensity aerobic exercise (AE) intervention or a health education control (HEC) comparison intervention. Follow-up interviews will be conducted at the end of treatment and at 3-, 6- and 12- month follow-ups. Based on the outcome of this preliminary trial, the exercise intervention will be further refined and readied for larger-scale clinical trials. PUBLIC HEALTH RELEVANCE: We expect that this project will result in the development of a well-specified, aerobic exercise intervention, the efficacy of which can be tested in future randomized clinical trials. Furthermore, we expect that this project will contribute much-needed knowledge about the role of aerobic exercise in reducing OCD symptoms, decreasing anxiety and depressive symptoms, and increasing psychosocial functioning, quality of life and cardiorespiratory fitness in OCD patients. If the efficacy of the AE intervention can be established, OCD patients who have clinically significant residual OCD symptoms following pharmacotherapy will be provided with a valuable treatment option for combating the deleterious effects of obsessive compulsive disorder, for which novel effective treatments are urgently needed and notably lacking.